Twin Spandau - Why did WW1 armaments stagnated at two guns?

[Avimimus]

Why did WW1 armaments stagnated at two guns? Why climb from one gun to two guns without keeping on going?

Was approximately 700-1000 rounds per minute optimal? Or did the balance between pilot/airframe and engine mean that twin guns were optimal for performance reasons? Or is the reliability offered by having a second gun the main reason?

I'm curious. Any more knowledgeable opinions?

 

[Lauge]

Why did WW1 armaments stagnated at two guns? Why climb from one gun to two guns without keeping on going?

Was approximately 700-1000 rounds per minute optimal? Or did the balance between pilot/airframe and engine mean that twin guns were optimal for performance reasons? Or is the reliability offered by having a second gun the main reason?

I'm curious. Any more knowledgeable opinions?

Don't know about "any more knowledgeable", but anyway....... There are two situations: fixed and movable guns.

For fixed guns, I think the two machine gun armament was the best compromise between mass, centre-of-gravity constraints, volume and damage potential. And two guns give you the advantages of robustness and rate of fire over just one.

For movable guns (as in those operated by an observer), anything more than two guns and their ammunition would probably be too cumbersome to be practical.

Just my 5 Eurocents worth. If you're interested in things like this, I can recommend the "Flying Guns" series of books by Anthony G. Williams & Emanuel Gustin

Regards & all,

Thomas L. Nielsen
Luxembourg

 

[Jemiba]

There were attempts to increase armament from the times of the Fokker E.III, I think,
as I remember having seen an experimental variant with 3 MG 08 on the nose. AFAIK,
this armament was aboned, because of the loss of performance. The Sopwith Dolphin
was another example for a 4-gun-fighter and, apart from engine problems, it was quite
succesful, I think, although in the Aeroplane article it was said, that the two additional
guns were often removed, IIRC.
But the two gun standard wasn't limited to WW I. If we look at many fighter of the early '30s,
they still had just 2 guns as well. Probably standard military doctrine just called for this
armament, which was felt to be sufficient. And the arrangement mostly was the same, the
guns in the nose, close to the gun sight, minimising parallax errors. And space in the aircrafts
nose was limited.
Just an attempt for an explanation, maybe it was just shortsightedness and persiting on traditions.

 

[Lauge]

Another factor is that, at a time when heavier-than-air flying machines were made from plywood, fabric and baling wire, a rifle caliber projectile was more than powerful enough to penetrate the fuselage and damage something vital (engine, fuel supply, pilot, etc.).

When air forces started transitioning to all-metal monoplanes with even a hint of ballistic resistance, the rifle caliber weapons quickly proved ineffective. In WWII both allied and axis aircraft showed progressively heavier armament as the war dragged on.

Regards & all,

Thomas L. Nielsen
Luxembourg

 

[Bill Garvin]

A related question that might answer the "two guns problem" as well. How were the machine guns fired? Did the pilot need to pull both triggers by hand? If so, there's the explanation for the two guns only question. Or was there a mechanism that allowed the pilot to fire both guns using one hand?

 

[Michel Van]

A related question that might answer the "two guns problem" as well. How were the machine guns fired? Did the pilot need to pull both triggers by hand? If so, there's the explanation for the two guns only question. Or was there a mechanism that allowed the pilot to fire both guns using one hand?

another reason was that the machine guns were synchronized to spinning propeller
by a Interrupter gear, so the guns fired without thrashing the propeller.

http://en.wikipedia.org/wiki/Interrupter_gear

but for a Interrupter gear to deal more as two guns, gets too complex and can fail. (for WW1 tech)

 

[Jemiba]

I think, the guns could always be fired from the control stick, here's a picture from
AirEnthusiast February 1972, showing german examples. But reaching the guns from
the cockpit was favourable for cocking, reloading and curing stoppages.

 

[Bailey]

But reaching the guns from the cockpit was favourable for cocking, reloading and curing stoppages.

Not just favourable, but a vital necessity...given the fact that jams were frequent.

According to H.F.King, Armament of British Aircraft, the Sopwith Dolphin was the World's first Multi-Gun Fighter. Two fixed Vickers and two free Lewis.

Regards Bailey.

 

[Jemiba]

"Not just favourable, but a vital necessity..." To support this :
Have looked again at the mentioned article about the Dolphin: Several were modified
to four fixed guns, two Vickers in the nose and two Lewis on the wings, but this modification
proved not to be really worthwhile, because the Lewis guns were drum fed and changing the
ammo drums wasn't possible in flight.
Some types had a single gun on the upper wing, but servicing in flight proved difficult, with the
pilot then standing in the cockpit (Sopwith Scout/Pub, I think).

 

[robunos]

But reaching the guns from the cockpit was favourable for cocking, reloading and curing stoppages.

Not just favourable, but a vital necessity...given the fact that jams were frequent.

This practice persisted until the 1930s...
I've finally found the picture of the prototype Hawker Hurricane, under construction, and
showing one of the Vickers guns, mounted at the side of the cockpit, and accessible to the pilot,
reproduced below. From Putnam's 'Hawker', page 38.

Some types had a single gun on the upper wing, but servicing in flight proved difficult, with the
pilot then standing in the cockpit

which is why the Admiralty Top Plane Mounting, and the Foster Mounting were devised,
to allow the Lewis gun to pulled down within the pilot's reach, and allow the ammo drum
to be changed.

pictures from 'Early Aircraft Armament: the aeroplane and the gun up to 1918', Harry
Woodman, Arms and Armour, pp.66-7.


cheers,
Robin.

 

[Avimimus]

Really interesting thoughts guys,

In terms of theses we now have four:
- The accepted wisdom/ministry policy hypothesis
- The interrupter gear hypothesis
- The excess weight hypothesis
- The reliability hypothesis

Some more research on three gun mounts in WWI:
- I've heard that the Sopwith Dolphin's extra guns were intended primarily for anti-bomber work and given mobile mountings for this purpose (including azimuth). In this sense it can be seen as being more properly two separate two gun mountings, rather than a proper four gun armament (although it is very interesting to hear that some pilots tried using all of the guns together).
- At least a few Caproni Ca.3s carried three ring mounted machinguns in a turret (A mounting that would require prohibitive strength to move)
- The revised Sopwith Salamander "trench fighter" was to have three guns (two depressed, one forward firing).
- S.E.5's were tested with a second Lewis gun over the wing and also with a three lewis gun oblique (45 degrees) upward firing installation. The Vickers Vampire was proposed to have a similar armament ( this was a pusher aeroplane).
- Several Fokker E.IVs were tested (including combat evaluations) with a three gun configuration leading to a performance loss and issues with inertial and gyroscopic forces. The interrupter gear failed and shot off the propeller during factory demonstrations. In addition Max Immelman apparently lost a propeller due to interrupter gear failures while using two gun Eindeckers (showing that this problem existed in multi-gun machines).

It is interesting that, among the above examples, only the Eindecker had the additional guns firing through the propeller - all other examples did not use synchronisation gear. This seems, along with the failure of the E.IV multiple interrupter gears, seems to support the interrupter gear argument. It is interesting to note that a larger percentage of WWII fighters didn't have weapons firing through the propeller arch and most of those which did use interrupter gear had only two guns (a notable exceptions being the Focke-Wulf 190, the G.55 and the Avia B.534 which had four synchonised guns).

It is very interesting to note that there were experiments with field modifications carrying three guns were tried, as well as scouts with flexible defensive guns etcetera - which calls into question whether it was purely a matter of ministry doctrine among all belligerents. The fact that aircombat was largely experimental, the number of belligerents and the varied small-scale manufacturers seems to make this unlikely. If three guns could be useful it would likely have been discovered. Of course, the slow development of armaments during the 1920s and 1930s, despite increasing speeds and durability, is likely due to this effect.

Examining the weight thesis: It would appear that two machine-guns were sufficient for bringing down enemy aircraft (although there were complaints about single gun installations not being effective enough and unsynchronised lewis guns remained in use despite their small magazines and inability to effectively reload in combat). The low power-to-weight ratios of aircraft during this period meant that additional armament would have caused real performance problems. It appears that 700rpm combined was the minimum for competitive combat effectiveness.

Does anyone know of examples where late war two-gun aircraft were field modified to have only a single gun armament?

Also, does anyone have an idea of the probability of one gun jamming in such a way that it couldn't be fixed in flight? Even when breaches could be cleared it might not have been possible while maneuvering or firing - so a twin gun armament may have increased reliability during the actual attack phase, where a single gun jamming wouldn't necessitate breaking off pursuit.

 

[Avimimus]

Discussing pictures.

Robunos: The picture is of a Hurricane mock up with two fuselage mounted fixed forward firing 0.303s? Correct?

Bailey: The picture shows the Dolphin's Lewis gun's at different angles - does this mean that only one gun could be used at a time (in which case it is properly a two-gun armament with two additional one gun stations)? Or were they fitted with a crossbar to link the two guns?

More info on the S.E.5. experiments: http://www.flightglobal.com/pdfarchive/view/1960/1960%20-%200194.html

 

[Jemiba]

The Dolphin was originally designed with two forward firing and two angled guns.
The latter ones are said to be disliked by many pilots and often removed. The four-
gun-all-forward arrangement seems to have been more or less a field modification.
The Salamander, AFAIK a development of the snipe, had two guns angled downwards,
firing through the armoured nose section and a single forward gun. Intention here was
to increase the time, ground targets could be hosed. So it wasn't a true multi gun armament
in our sense, I think.
In the cases of guns firing out of the propellor arc: Were they already adjusted to converge
their fire in a ceartin distance, or were they just mounted parallel? I can imagine, that aiming
such a weapon would have been much more tricky then, as firing distances may still have been
lower.

 

[robunos]

Robunos: The picture is of a Hurricane mock up with two fuselage mounted fixed forward firing 0.303s? Correct?

it's the actual Hurricane prototype, under construction. Armament was to have been four machine guns; this from
Putnam's 'Hawker', page 286 :-

"...a new specification, F.36/34, was drafted around the design as it stood in August, 1934...
The F.36/34 design was accepted and in February 1935...
manufacture of a prototype to have... an armament of four guns - a Vickers gun on each side
of the nose, and either a Browning or Vickers gun in each wing. Arguments in favour of a
heavier armament were, however, accepted and the contract was amended to provide for the
inclusion of...eight Browning machine guns."

Bailey: The picture shows the Dolphin's Lewis gun's at different angles - does this mean that only one gun could be used at a time (in which case it is properly a two-gun armament with two additional one gun stations)? Or were they fitted with a crossbar to link the two guns?

If I may...
From Putnam's 'Sopwith', page 208 :-

"Details of how the Lewis guns were to be installed...and to limit the training (aiming) of these guns a three position
ratchet was the approved fitting.The extent to which two Lewis guns were actually fitted as well as the two 'built-in'
Vickers, remains unclear; although a single Lewis was far more common in the field, a familiar picture of ...C3786...
with both Lewis guns fitted, while others have their Vickers guns only..."

The revised Sopwith Salamander "trench fighter" was to have three guns. This was a pusher aeroplane.

The Sopwith Salamander was *never* a pusher design. I think you are confusing the Salamander with the Vickers FB.26
Vampire, which *was* a pusher, and *was* tested with the Eeman triple gun mounting.

The Salamander, AFAIK a development of the snipe, had two guns angled downwards,
firing through the armoured nose section and a single forward gun.

The Salamander was originally intended to have this armament arrangement, but following evaluation of the similarly armed
Sopwith TF.1 Camel, it was decided that this armament scheme was unworkable, and the Salamander's guns were re-arranged
as two forward firing Vickers guns. See 'the First British Armoured Brigade', Air International, March 1979, pp.149-153, and
April 1979, pp.182-190, and pp.199-200.
The Salamander was a development of the Snipe, although with a strengthened structure to cope with the added weight of the
armour. It was fortunate that the war ended when it did, for in December 1918, it was discovered that a large number of the
Salamanders thus far built had been fitted in error with Snipe centre-sections, which rendered the aircraft dangerously weak.
Fortunately, they could be grounded without any problems...


cheers,
Robin.

 

[Avimimus]

Thanks for the clarifications.

The Sopwith Salamander was *never* a pusher design. I think you are confusing the Salamander with the Vickers FB.26
Vampire, which *was* a pusher, and *was* tested with the Eeman triple gun mounting.

100% - Exactly what I had intended to think.

 

[Avimimus]

Found some relevant information on jams (nicely prepared by Squid and carefully written by Leon Bennet):

In the spirit of all that is just and holy, lets take a look at what Leon Bennet has to say on the matter (Author of Gunning For the Red Baron.)

"Shooters new their guns to be complex assemblies of tricky parts. Every course of instruction offered some takedown and reassembly experiance, with the emphasis on stoppages and fast cures. The unexpected part was the realisation of how frequenlty even the best regulated guns refused to work, and of how little there was to be done about it at lubricant-freezing, oxygen poor altitudes."

"The establishment did offer some support to worried shooters. British Royal Navy Air Service (RNAS)squadrons maintained an official inspection jig constisting of a spare gun pointed straight down along with approved instructions. "Drop the cartrigdes down one by one...if they go home they are satisfactory and can be loaded into the magazines"

The test was of some use, for those cartridges refusing to drop all the way home were oversized or bent. However this test was to cartridge health as a military board examination was to soldiers health - Stong in an easily checked detail, weak in all that was passed over. There was no test for split cartridges, corroded brass, defective primers or undersized parts. It was all upto the inspectors intuition and mood. Not surprisingly, after a stoppage or two most shooters prefered to do their own inspection.

The jammed gun issue never ended. Approximatley once a month, in combat, one or both guns would refuse to fire, leaving the shooter defensless. Truely odd where those occasions when a paired Lewis and vickers machine gun would fail simultaneously, though independant in design, location and means of triggering. Simultaneous jamming of unrelated guns (e.g., SE5a) suggested lubrication failure owing to the extreme cold of high altitude or perhaps a literal freezing as cloud droplets turned to ice.

"Although weather problems were real, many more jams reflected the inability of old gun designs to adapt to the newer smokeless powders. Both Vickers and Spandau guns were descendents of Maxim's original design, all born in black powder days. With the advent of smokeless powder came less smoke and much more gas pressure, serving to add to muzzle velocity and flatten trajectory. These were useful triats. Unfortunately, the new, higher internal gas pressure decayed slowly after firing; certainly much more slowly than with black powder. On the one hand, when it came time to eject the fired case, a great deal of pressure still exsited in the barrel, acting to press the case against its seat. Ejecting a case forcibly held in place by gas pressure was not a simple matter. An important either-or design decision was necessary and the winning design consideration was a high rate of fire. The price was an awesome number of jammed guns.

To eject a brass case pinned to its firing chamber by gas pressure took a most determined yank. Extreme force was availible to gun designers and they had little difficulty in assembling the necessary lobes, cams, and catches. The difficulty was the brass case. Offering no match for the extreme loads of expulsion, the thin brass tended to rip apart. At high altitudes, the cold temperatures lowered the strenght of the basic metal brass and froze whatever grease might have been availible to serve as a friction reducing lubricant. The effect was to further increase the already large yanking force whilst simultaneously reducing the cartridge case's ability to withstand the yanking stress. The result was inevitable - broken cartridge cases.

Actually, a fractured case didnt matter - so long as every bit of it was ejected. Difficulties arose when bits where broken off and left behind. Then the next round to enter would wedge the broken bit between cartridge and firing chamber. The bolt couldnt close and, as a saftey measure the gun couldnt fire. The result was a sever jam. There was still a chance: working the charging handle might eject a broken case. However, even a few pumps of the Vickers charging handle meant disconnecting a feed belt, and then hooking it up again, a matter of additional lost time. As a last straw, the removal process handled broken bits ineffectively and it could take eight or more trys to get the all the peices out.

Consider the shooters mindset. His attack has failed, along with his guns. An aroused enemy is out for blood. In the midst of life threatening combat, the shooter is to un-hook belt feeds, work the charging handles, and then hook up the belt feeds, only to discover there were apparently more broken bits inside the firing chambers and the cursed guns still wont fire...Once can easily picture the rage of shooters afflicted with gun jams

Finally, there was a monumental form of jam in which the wedging action proved so solid and complete that the charging handle itself was stuck. In this instance, the classic Lewis #4 jam (of 6!), official advice was to dissasbemle the gun "while the obstruction is picked out with the point of a bullet or spike of a knife".


The remaining jam types resulted from wear, breakage, and improper adjustments of and extremly complex mechanisim. In choosing between the Vickers and Lewis, the gas operated Lewis was likely simpler than the recoil operated Vickers, but even a quick summary of Lewis working concepts shows an ample opening for Murphys Law to work its chaos.

As all lewis fire was fully automatic, single shots were impossible. To prevent overheating the barrel, a burst of five rounds was standard, though in combat, ten was more likely and in an all out crisis the entire forty-seven-round drum could be emptied in five seconds after certain adjustments to the clock spring torsion, increasing the cyclic rate. The process of emptying a drum at one go would almost certianly result in a "blued" barrel, or one whose steel temper had been lost, in turn yeilding to wildly inaccurate shooting.

As compared to the Lewis, the recoil based Vickers enjoyed a much greater and longer development period - more than a generation - suffecient to work the bugs out of its unlikely collection of mechanical parts. The result was a fixed gun of almost twice the Lewis weight, able to fire hundreds of cartridges in short bursts, and all without the interruptions of the drum changing sort.

However, along with the powerful Vickers advantages came worrisome disadvantages. For example, the belt feed that provided continuous fire created horrendous jams, should the hemp-based belt stiffen and freeze at altitude. Combat proved that Lewis drums to be good or better in withstanding extreme cold. A solution in the form of a belt made of metal links, neatly spacing the cartridges and weatherproof to boot, was developed some two years into the war, but as a dissapointed Col. Sefton Brancker wrote to Gen. Hugo M Trenchard (July 1916) " the articulated belt is made of too soft a metal and the clips are subsequenly jamming".

Okay thats a lot of information there, and I hope you have the patience to read through it all. I enboldened the most pertinant points.

So reliability may have been an even greater factor than firepower.

 

[Mike OTDP]

Weight was a big factor. A Vickers ran ~35 lbs...plus ammo. Ammo could easily weigh more than the gun. From a military perspective, two rifle-caliber MGs were adequate.

 

[robunos]

I've been doing a bit of further reading round this topic, and it seems that development was not quite as 'stagnant' as was possibly first thought. Rather, it seems a though the demand to maintain production, extended the development cycle to the point where the Armistice intervened before the next wave of weaponry could be deployed.

On the Allied side, in the British case, the Vickers had been improved constantly, with the adoption of the Hazleton muzzle attachment, to increase the rate of fire, along with the US developed 'speeding-up spring'. Also, in 1918, following the appearance of armoured aircraft, the Vickers was bored out to .50 calibre, but was not really successful.
Also, the aircraft makers were looking to increase the number of guns fitted to their airframes. In particular, the Sopwith Snark, a triplane designed in early 1918, was to have, in addition to it's two synchronised Vickers, no less than four Lewis guns, mounted in pairs, under the bottom wing, firing outside the propeller arc.

The French, meanwhile, were developing a fully automatic version of their 37mm Puteaux cannon, firing through the propeller shaft of the 200hp Hispano-Suiza. The earlier semi-auto version was used with some success by French pilots in the Spad 12Ca1, using both canister and explosive ammo. However, this weapon would not be available in any quantity before the war's end.

It was, however, the entry of the United States into the war which produced the greatest potential for increased firepower for Allied aircraft.
Firstly was the availability of the Colt Browning model 1918. In July 1918, one of these guns was tested on a Bristol Fighter and found to be superior to the standard Vickers, but was not adopted due to the end of hostilities. Also, as with the Vickers, a .50 calibre version was developed, at the personal request of General Pershing, in order to increase firepower against armoured aircraft and vehicles. This in time would become the famous 'Browning 50 cal'.
However even in US service, the Browning was eclipsed by the Marlin, originally intended as stopgap until the Browning was ready, but so successful that the Browning took second place. Developed from the 1895 Colt 'potato digger', it proved effective and reliable. It was the first gas operated gun to be reliably synchronised, one aircraft being fitted with no fewer than four guns. The French were impressed with this gun, and it seems that they were looking to replace the Vickers with this weapon on newly-built aircraft, had the war not ended.

Regarding the Central Powers, in Germany's case, in early 1918 the development was begun of the 'TuF' (Tank und Flieger) gun, again in response to the appearance of armoured aircraft and vehicles. Derived from the LMG08/15 'spandau', calibre was increased to 12.7mm, and the 770 grain round was fired with a muzzle velocity of 2,650 fps. When used with armour piercing ammo it proved capable of penetrating Allied tanks at up to 100 yds range. 4,000 of these guns had been built by the cessation of hostilities.
The Becker 20mm cannon was also available for aircraft use.

Link to Becker patent :-
http://patimg2.uspto.gov/.piw?Docid=01144285&idkey=NONE

In the case of Austria Hungary, something even more fearsome was in the works.
In 1917, Ferenez Gebauer devised an engine driven machine gun. Three prototypes were built, and one of them was tested at the Fighter Trials held in June 1918. It performed well, and was ordered into production. The first of these were available for installation as the war ended.
This weapon was actually a twin barrelled gun, capable of a maximum combined cyclic rate of fire of 1600 rpm. Calibre was 8mm.

Link to Gebauer gun patent :-

http://v3.espacenet.com/publicationDetails/biblio?DB=EPODOC&adjacent=true&locale=en_EP&FT=D&date=19260729&CC=GB&NR=250233A&KC=A

So, putting on our 'Luft '19' glasses, we see RAF fighters armed with Vickers/Brownings, and multiple Lewis guns, and US planes carrying several Marlins, or .50 calibre Brownings, tangling with TuF equipped German aircraft, while French 37mm cannon armed Spads attack German bombers defended by Becker cannons and Gebauer equipped escorts.

sources :- 'Early Aircraft Armament', 'British Aircraft Armament Vol.2', and Putnam's 'Sopwith'


cheers,
Robin.

 

[Bailey]

Interesting research Robin, many thanks for sharing it.

Cheers Bailey.

 

[riggerrob]

Found some relevant information on jams (nicely prepared by Squid and carefully written by Leon Bennet):

"... British Royal Navy Air Service (RNAS)squadrons maintained an official inspection jig constisting of a spare gun pointed straight down along with approved instructions. "Drop the cartrigdes down one by one...if they go home they are satisfactory and can be loaded into the magazines"

The test was of some use, for those cartridges refusing to drop all the way home were oversized or bent. However this test was to cartridge health as a military board examination was to soldiers health - Stong in an easily checked detail, weak in all that was passed over. There was no test for split cartridges, corroded brass, defective primers or undersized parts. It was all upto the inspectors intuition and mood. Not surprisingly, after a stoppage or two most shooters prefered to do their own inspection.

The jammed gun issue never ended. Approximatley once a month, in combat, one or both guns would refuse to fire, leaving the shooter defensless. Truely odd where those occasions when a paired Lewis and vickers machine gun would fail simultaneously, though independant in design, location and means of triggering. Simultaneous jamming of unrelated guns (e.g., SE5a) suggested lubrication failure owing to the extreme cold of high altitude or perhaps a literal freezing as cloud droplets turned to ice.

"Although weather problems were real, many more jams reflected the inability of old gun designs to adapt to the newer smokeless powders. Both Vickers and Spandau guns were descendents of Maxim's original design, all born in black powder days. With the advent of smokeless powder came less smoke and much more gas pressure, serving to add to muzzle velocity and flatten trajectory. These were useful triats. Unfortunately, the new, higher internal gas pressure decayed slowly after firing; certainly much more slowly than with black powder. On the one hand, when it came time to eject the fired case, a great deal of pressure still exsited in the barrel, acting to press the case against its seat. Ejecting a case forcibly held in place by gas pressure was not a simple matter. An important either-or design decision was necessary and the winning design consideration was a high rate of fire. The price was an awesome number of jammed guns.

To eject a brass case pinned to its firing chamber by gas pressure took a most determined yank. Extreme force was availible to gun designers and they had little difficulty in assembling the necessary lobes, cams, and catches. The difficulty was the brass case. Offering no match for the extreme loads of expulsion, the thin brass tended to rip apart. At high altitudes, the cold temperatures lowered the strenght of the basic metal brass and froze whatever grease might have been availible to serve as a friction reducing lubricant. The effect was to further increase the already large yanking force whilst simultaneously reducing the cartridge case's ability to withstand the yanking stress. The result was inevitable - broken cartridge cases.

Actually, a fractured case didnt matter - so long as every bit of it was ejected. Difficulties arose when bits where broken off and left behind. Then the next round to enter would wedge the broken bit between cartridge and firing chamber. The bolt couldnt close and, as a saftey measure the gun couldnt fire. The result was a sever jam. There was still a chance: working the charging handle might eject a broken case. However, even a few pumps of the Vickers charging handle meant disconnecting a feed belt, and then hooking it up again, a matter of additional lost time. As a last straw, the removal process handled broken bits ineffectively and it could take eight or more trys to get the all the peices out.

Consider the shooters mindset. His attack has failed, along with his guns. An aroused enemy is out for blood. In the midst of life threatening combat, the shooter is to un-hook belt feeds, work the charging handles, and then hook up the belt feeds, only to discover there were apparently more broken bits inside the firing chambers and the cursed guns still wont fire...Once can easily picture the rage of shooters afflicted with gun jams

Quality of British ammunition deteriorated during WW1.

Quality of British ammunition deteriorated rapidly during WW1. As tooling wore out, shells slowly increased in diameter. Under pressure to produce millions of rounds per month, factory inspectors allowed quality control standards to relax.
This resulted in sloppily-built British .303 ammo jamming in precisely-built Canadian Ross Rifles. The Canadian Army soon learned how to re-bore chambers in Ross Rifles to accommodate the sloppy ammunition, but the damage to the Ross Riffles' reputation had been done.
Corrosion was a problem for trench-fighters, but the RFC hoped to fire all its ammo before it had time to corrode.